diff --git a/requests/sessions.py b/requests/sessions.py
index aa956d3f..c4937752 100644
--- a/requests/sessions.py
+++ b/requests/sessions.py
@@ -9,7 +9,7 @@ requests (cookies, auth, proxies).
 
 """
 import os
-from collections import Mapping
+from collections.abc import Mapping
 from datetime import datetime
 
 from .compat import cookielib, OrderedDict, urljoin, urlparse
@@ -127,12 +127,14 @@ class SessionRedirectMixin(object):
                 prepared_request.body = None
 
             headers = prepared_request.headers
-            try:
-                del headers['Cookie']
-            except KeyError:
-                pass
-
-            prepared_request.prepare_cookies(self.cookies)
+            # Only delete 'Cookie' header if there are no cookies to send
+            if len(self.cookies) == 0:
+                try:
+                    del headers['Cookie']
+                except KeyError:
+                    pass
+            else:
+                prepared_request.prepare_cookies(self.cookies)
 
             resp = self.send(
                 prepared_request,
